The present study sought to extend the literature by examining age of onset of tobacco and marijuana use as well as regular drinking. In addition, youth were followed over an extensive period of time through key developmental phases associated with substance abuse risk. Research has indicated that early adulthood is a high risk period for the development of substance use problems because it involves multiple contextual changes and changes in social roles within a brief developmental window.22 As the individual makes the transition into early adulthood, multiple systems of the individual and the context enter a period of temporary flux.23 Because this transition occurs within a short developmental window, marked by extensive change,22 it may be particularly challenging for some youth. As youth negotiate these major changes, they may rely on substance use to cope. Indeed, research has shown that alcohol use accelerates during adolescence, peaks during early adulthood, and subsequently decreases.24 Clinical substance abuse and dependence similarly peak between 18 and 23 years of age.25,26 Importantly, the design of this study allowed for alcohol use and abuse to be
